I've mounted a brand new engine and when trying to slip the prop on the threaded engine shaft the fit is so tight I can't get it on.
I tried both a wooden and nylon prop and both do the same thing. Are they supposed to be that tight and if so, how do you get them on?
I don't want to hammer in fear of damaging the engine but no matter how hard I push it won't go on. Please help!! Thanks.

You need a Prop Reamer to enlarge the hole in the Prop.

http://www3.towerhobbies.com/cgi-bin...amer&search=Go

Hi!
Just use a round file ! Don't hammer anything!
But...Seems strange to me that your prop is hard to mount. Most of the time the it just slips on.
What kind of strange engine do you have???

Thanks, Guys,

I have an OS Max 46AX brand new engine with Master Aircraft 11x6 Nylon props, also brand new. I tried an old Top Flight wooden prop I had laying around and the same thing.

I have had to ream every prop I have had. on all different engines. get a prop reamer, there cheap and fit into your box easy. please dont try to drill it. it will get off center

The prop reamer is a must. It is the only way to keep the hole centered correctly. Now comes the rub, you need two, a fraction and a metric.

Most props start life with a 1/4" bore. THis fits most smaller engines, but some engines have a metric size prop shaft, IE a saito. The Magnum 52 and the O.S 52 four strokes have a 1/4" shaft, THe Magnum 70 and 91 four strokes have a 5/16" shaft. My saito four stroke has a shaft in MM, don't remember the size.

Towere sells both a metric and fractional reamers, both with a 1/4" pilot on them. They are money well spent.

The prop should fit with a frictioin fit to the shaft. IE slide over the thread, but get a slight resistance when it goes on the shoulder on the prop shaft near the hub. Usually a well fit prop will spin on up to the hub, but be a little slugish to push on. A loose fit prop is a problem waiting to happen, No mater how well you balance the prop, it is all but impossible to get it centered, so it will run out of balance. This is hard on the plane and on the engine.

I picked up a batch of 12x6 Zinter wood props on Ebay when I first started flying, It turns out that they were all bored to 0.260", a sloppy fit on the engine. I made a thin bushing from 0.005" brass shim stock and they were fine after going that route. I also used the same size prop on the 52 and 70 four strokes, so I reamed them out to a 3/8 and then made a set of bushings for 1/4" 5MM and 5/16" shafts and I could swap probs at will.

Don

There is nothing strange or unusual about your engine or your props. A stepped prop reamer in SAE if applicable or a metric (as linked above) if needed should be in every flyers box and used with any new prop as outlined by Campgems.

Never try to screw them on with the threads or file and/or drill the hole.

John

Thanks, Guys,

Can a prop reamer be used on a nylon prop?

Absolutely.

Ken

I gather it is something called an "OS". Strange indeed. Ever heard of one?

jess

I picked a new APC 10x6 out of my stock and tried to slip it on my Saito 45. It went over the threads OK, but not over the sholder. I put my reamer on it and it took quite a cut to get to 1/4". So, the engine isn't the isue, but the props may be tight and need reaming to 1/4"

There are a few things I would like to point out about reaming the props, and I'll focus on the APC props. As I pointed out above, they may run tight in the bore. This is good because I would rather have a prop that I could ream to size vs one that I had to use bushings on.

The prop reamer is a "Hand Reamer", with stepped sizes. If you chuck this reamer in the drill press and poke it through a prop, a couple things may happen if your drill press chuck isn't running very true, the table is not trammed to the chuck spindle, and you don't have a good fixture setup to keep the drive surface of the prop aligned correctly, your reamed prop may have an over sized hole, and one that doesn't track to the orginal bore. By reaming by hand, and from the right direction on the prop, the piilot on the reamer will keep the reamer running true to the orginal bore.

When reaming the prop, never back up the reamer. The fit to the reamed hole is zero clearance and if you back up the reamer, you stand a very good chance of picking up some swarf and locking the reamer in the prop. Also backing a reamer up destroys the cutting edge. Remember, these props are glass reinforced plastic, so they are quite abrasive to tool steel.

The APC props are cast with a larger bore at the back of the prop than the bore in to front. To get things going straight, start the reamer from the back. This gives the longest guidance for the pilot, all the way to the point the next step penetrates the front surface.

After you ream the prop to the size, contiue turning the reamer in until you get a slight chamfer from the next step. THis cleans any flashing on the hole and allows the cones of the prob blancer to fit accuratly to the bore. When you remove the reamer, continue to turn it clockwise, not backing it up. Now feed it in from the front and again cut a slight chamfer where the reamer exited the face of the prop. There will be a lot of flashing here and you need a good clean base for your balancer to work from.

I took some photos of the reamer in action poking a 5/16" hole through a prop that was fit for a 1/4" shaft ogrinally. Note the broken end[>:]

Sorry about a couple of photos not focused well, but I think you will get the idea

Don

Prop reamers also work great in enlarging holes in kit parts. But do it gradually, as it cuts very quickly.

Campgems said it perfectly

Yeah, what is that? Never heard of them! Both my nylons needed reaming, but my apc went right on.